1. Technical Field
The present disclosure relates to electrosurgical instruments for open, percutaneous, endoscopic, or laparoscopic surgical procedures. More particularly, the present disclosure relates to a radiofrequency tissue ablation system having multiple, independently-phased electrodes for providing rapid energy delivery and improved ablation control.
2. Background of Related Art
The use of electrical energy including radiofrequency and microwave energy and, in particular, radiofrequency (“RF”) electrodes or microwave antennae for ablation of tissue in the body or for the treatment of pain is known. Generally, RF electrodes (e.g., probes, resistive heating elements, and the like) include an elongated cylindrical configuration for insertion into the body to target tissue that is to be treated or ablated. The RF electrodes can further include an exposed conductive tip portion and an insulated portion. The RF electrodes can also include a method of internal cooling, such as the RF electrodes shown and described in U.S. Pat. No. 6,506,189 entitled “COOL-TIP ELECTRODE THERMOSURGERY SYSTEM” issued to Rittman, III et al., on Jan. 14, 2003 and U.S. Pat. No. 6,530,922 entitled “CLUSTER ABLATION ELECTRODE SYSTEM” issued to Cosman et al., on Mar. 11, 2003. Accordingly, when the RF electrode is connected to an external source of radiofrequency power, e.g., an electrosurgical generator (device used to generate therapeutic energy such as radiofrequency, microwave, or ultrasonic), and current is delivered to the RF electrode, heating of tissue occurs near and around the exposed conductive tip portion thereof, whereby therapeutic changes in the target tissue, near the conductive tip, are created by the elevation of temperature of the tissue.
In some applications, for example, tumor ablation procedures, multiple electrodes may be inserted into the body in an array to enlarge ablation volumes. In a particular application, arrays of high frequency electrodes are inserted into tumors. The electrodes are typically placed in a dispersed fashion throughout the tumor volume to cover the tumor volume with uniform heat. In one common arrangement, the electrodes are arranged in a delta (i.e., triangular) configuration. The multiple electrodes may be activated simultaneously or sequentially with high frequency energy so that each electrode heats the surrounding tissue. Simultaneous activation allows maximum energy to the applied to the tissue, but may also have drawbacks. Current from the electrodes tends to travel away from the electrode array, causing an isopotential area or volume, (i.e., a dead zone), to form between the electrodes. Such an isopotential area may result in incomplete ablation of targeted tissue because insufficient energy is delivered to the isopotential region. Series activation, wherein energy is applied to fewer than all electrodes at a time (typically one or two electrodes at a time) can prevent the formation of an isopotential region between the electrodes. However, the sequence of cycling energy through the electrodes in this maimer may also have drawbacks, because it limits the rate of energy delivery into tissue.